1. Field of the Invention
The present invention relates to a card slot unit, its manufacturing method and a computer apparatus.
2. Description of the Related Art
In general, in a personal computer, also referred to hereafter simply as a PC, particularly in a portable PC such as a notebook PC and a small-size information apparatus, there is provided a card slot unit for mounting cards in most of the equipment so that a function extending card can be utilized for realizing the functional extendibility of the equipment. In recent years, such a card slot unit is becoming indispensable with the popularization of the PC. Function extending cards are not limited to that having simply an added value of a memory card. Function extending cards offering added values offered by cards such as a facsimile-modem card, an SCSI (Small Computer System Interface) card, a hard-disk interface card, a LAN (Local Area Network) adapter card, a tuner-adapter card and a camera-adapter card become available, widening the range of applications of the card slot unit.
FIG. 1 is a block diagram showing a typical configuration of a PC having a card slot unit of the type described above.
As shown in the figure, a card slot unit 2 is built inside the main body 1 of a PC. A function extending card 3 such as a PC card can be plugged into the card slot unit 2. In general, the configuration of the card slot unit 2 comprises a slot board 4 serving as a base and a slot connector 5 mounted on the slot board 4 as shown in FIG. 2. The slot connector 5 is a part serving as contact with the function extending card 3. Signals from the function extending card 3 are supplied to a card control device 6 shown in FIG. 1 through a wiring pattern of the slot board 4 which is not shown in the figure. The card control device 6 is mounted on a main board, which is also not shown in the figure, along with a CPU chip (a microprocessor) 7, a memory/bus controller 8 and a main-storage chip 9. A system bus 10 connected to the CPU chip 7 is created on the main board. The card control device 6 and the memory/bus controller 8 are also connected to the system bus 10.
In a PC system having the configuration described above, the function extending card 3 is plugged into the card slot unit 2, providing an additional function to the main body 1 of the PC. In this arrangement, signals are exchanged between the function extending card 3 and the main body 1 of the PC by way of signal wires extended through the card slot unit 2 and the card control device 6.
In the above embodiment, by the way, all controllers are traditionally mounted on the main board of the PC main body 1 on which the system bus is created. In addition, in order to make the assembly work convenient, IC chips and other parts are all mounted on the main board. Because of these reasons, the card control device 6 is mounted at a location in close proximity to the system bus 10. In such an arrangement, however, wiring on the card slot unit 2, wiring on the main board and a means for connecting them to each other are required. As a result, a wiring path from the function extending card 3 plugged in the card slot unit 2 to the card control device 6 on the main board becomes long and the inductance (L) as well as the capacitance (C) of signal lines between them also increase as well. In such a structure, when a signal with a high frequency such as a moving-picture signal 1 is input through the function extending card 3, in particular, the waveform of the signal becomes distorted and noise or the like affects the signal, giving rise to a problem that an error is generated.
As a measure for countering the problem described above, reduction of the output impedance generated by the function extending card 3 is conceivable. In order to reduce the output impedance of the function extending card 3, however, it is necessary to increase the electrical capacitance of the card control device 6 for controlling the function extending card 3. It is thus necessary to increase the area on the surface of the expensive main board which is occupied by the card control device 6. As a result, the card control device 6 itself also becomes expensive, giving rise to a considerable increase in cost. In addition, with such a measure, the current output through the terminal of the card control device 6 also increases, leading to an increase in current consumption which is a disadvantage for a portable information apparatus because an increase in current consumption will shorten the life of the battery.